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The Menstrual Cycle

The Menstrual Cycle. Oogenesis. In the ovary. Timeline. Feedback. Click image to continue. Quit. Germinal epithelium (layer of cells surrounding ovary). Blood vessels. Home. Quit. Growing oogonium Formed by mitosis from cells in the germinal epithelium. Home. Primordial follicle

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The Menstrual Cycle

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  1. The Menstrual Cycle Oogenesis In the ovary Timeline Feedback Click image to continue Quit

  2. Germinal epithelium (layer of cells surrounding ovary) Blood vessels Home Quit

  3. Growing oogonium • Formed by mitosis from cells in the germinal epithelium Home

  4. Primordial follicle • Primary oocyte is surrounded by a single layer of follicle cells • 7 million formed before birth. Only 450 will reach ovulation. Home

  5. Primary follicle • FSH activates primordial follicle. • Follicle cells divide to form many layers. Home

  6. Ovarian development Secondary follicle • Ovary adds layer of cells (theca) outside the follicle cells. • Both layers secrete female hormones into fluid-filled spaces. Home

  7. Graafian (mature) follicle • Grows to about 10mm diameter due to stimulation by oestrogen. • Seconday oocyte and 1st polar body formed after surge of LH Home

  8. Ovulation • Surge in LH causes Graafian follicle to release secondary oocyte. • Secondary oocyte carried into fallopian tube. Home

  9. Corpus luteum (yellow body) • Formed from remains of the Graafian follicle. Its growth is stimulated by LH. It secretes Progesterone (and some Oestrogen). Home

  10. Corpus luteum degenerates • If fertilisation does not occur, the corpus luteum degenerates. • Probably due to chemicals it releases itself. Home

  11. Corpus luteum degenerates • If fertilisation does not occur, the corpus luteum degenerates. • Probably due to chemicals it releases itself. Home Quit

  12. The ovarian cycle repeats every 28 days Home Quit

  13. Time The ovarian cycle repeats every 28 days Home Quit

  14. LH FSH Oestrogen Progesterone The ovarian cycle repeats every 28 days due to a sequence of hormonal changes controlled by feedback - both negative and positive. Home

  15. LH FSH Estrogen Progesterone Uterus lining Home The hormonal changes affect other organs in the body too.

  16. FSH levels rise LH FSH Estrogen Progesterone Home

  17. FSH levels rise This is repeated 28 days later LH FSH Estrogen Progesterone and stimulate the development of a primary follicle in the ovary Home

  18. Rising estrogen levels inhibit FSH secretion by the anterior pituitary LH FSH … estrogen levels rise Estrogen Progesterone The follicle cells produce Estrogen Home

  19. Rising estrogen levels inhibit FSH secretion by the anterior pituitary LH FSH … estrogen levels rise Estrogen Progesterone Rising estrogen levels also stimulate repair and development of the uterus lining Home

  20. LH FSH Estrogen rises to a high concentration Estrogen Progesterone The follicle continues to grow and mature Home

  21. … and stimulates the anterior pituitary to release LH and FSH LH FSH Estrogen rises to a high concentration Estrogen ... and development of the corpus luteum Progesterone The surge in LH causes ovulation Home Notice that estrogen stimulates at high concentration (Positive Feedback)

  22. Both estrogen and progesterone levels rise LH FSH Estrogen Progesterone The corpus luteum secretes progesterone (and some estrogen) Progesterone causes the uterine epithelium to store glycogen and stimulates blood vessel growth Home

  23. … this inhibits LH and FSH secretion by the anterior pituitary Both estrogen and progesterone levels rise LH FSH Estrogen … which prevents another follicle maturing Progesterone Home

  24. LH FSH Estrogen Progesterone … and progesterone (and estrogen) levels fall. If the egg is not fertilised, the corpus luteum degenerates Home

  25. FSH secretion is no longer inhibited and its level rises LH FSH Estrogen Progesterone … and progesterone (and estrogen) levels fall. The uterus lining is not maintained and menstruation occurs

  26. FSH secretion is no longer inhibited and its level rises LH FSH Estrogen Loop Progesterone … and progesterone (and estrogen) levels fall. The uterus lining is not maintained and menstruation occurs Home Quit

  27. Pituitary gland Back Home Quit

  28. Hypothalamus Portal vein Anterior pituitary gland Home Quit

  29. Neurosecretory cells release Gonadotrophin Releasing Hormone into a small vein Home

  30. GnRH diffuses to cells in the anterior pituitary. … and stimulates the release of FSH. Home

  31. Back GnRH diffuses to cells in the anterior pituitary. … and stimulates the release of FSH. FSH is carried in the blood to the ovary. Home Quit

  32. H/P Home Quit

  33. Hypothalamus Anterior Pituitary Gland H/P Ovary Uterus Home Quit

  34. GnRH stimulates release of FSH by the anterior pituitary gland Home

  35. At this level estrogen inhibits FSH secretion FSH stimulates the development of a follicle Estrogen levels rise and stimulate repair and development of uterus lining Home

  36. At high levels estrogen stimulates LH (& FSH) secretion This causes a surge in LH The follicle continues to grow and release estrogen Home

  37. Progesterone and estrogen inhibit LH and FSH secretion This causes a surge in LH ... which causes ovulation Progesterone levels rise and stimulate glycogen storage and blood vessel proliferation in the uterus ... and the formation of the corpus luteum Home

  38. Progesterone levels fall and no longer inhibit FSH secretion If it doesn’t receive the hormone ‘HCG’ from an embryo, the corpus luteum degenerates Progesterone levels fall and menstruation occurs Home

  39. Progesterone levels fall and no longer inhibit FSH secretion Home Loop Quit

  40. Primordial Germ Cell (2n) Home Quit

  41. Primordial Germ Cell (2n) Mitosis Oogonia (2n) Mitosis Many Oogonia (2n) Timing Growth Primary Oocyte (2n) Meiosis I 1st Polar Body (n) Secondary Oocyte (n) Meiosis II 1st and 2nd Polar Bodies (n) Ovum (n) Home Meiosis I stops at prophase throughout childhood Meiosis II stops at metaphase until fertilisation Quit

  42. Found in the germinal epithelium of embryos aged 4 to 8 weeks Primordial Germ Cell (2n) Oogonia (2n) Found in the ovary when the foetus is aged between 5 and 30 weeks Many Oogonia (2n)  7 million when the foetus is aged 20 weeks. 2 million at birth. Primary Oocyte (2n) 1st Polar Body (n) 450 reach ovulation Secondary Oocyte (n) 1st and 2nd Polar Bodies (n) Ovum (n) Home Quit

  43. Primordial Germ Cell (2n) Oogonia (2n) Many Oogonia (2n)  Primary Oocyte (2n) 1st Polar Body (n) Secondary Oocyte (n) 1st and 2nd Polar Bodies (n) Ovum (n) Home Quit

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